Recently, a demand of changing the color of hairs to a lighter color is increased in response to the change in the consumer's mind, resulting in an expansion of the hair dye market.
A hair dye consists of a first agent containing an alkaline agent and an oxidation dye and a second agent containing an oxidant, and is used first by mixing the first and second agents upon coloring operation, and then applied onto hairs, allowed to stand, and then rinsed (see FIG. 1).
Conventionally, ammonia is employed usually as an alkaline agent. While the ammonia has sufficient decolorizing performance, dying performance and color-lasting performance, it exhibits an intense irritative odor, which gives a substantial discomfort upon coloring operation, sometimes causes an eye irritation. It also causes a stiffness on the hair occasionally after the coloring operation.
Accordingly, it was attempted to use an alkali having a reduced irritative odor instead of the ammonia. For example, a method employing a basic amino acid (JP-A-59-106413), a method employing a guanidium salt (JP-A-11-180837) and a method employing a carbonate (JP-B-7-59490) are well known.
However, any of these methods has an insufficient decolorizing performance and can not be successful in dying the hairs a light color tone, although it can overcome the problems associated with the irritative odor. It also has an insufficient dying performance, and suffers from a difficulty in dying the hairs a deep color, to which a solution has been desired.